Empty+and+foam-filled+circular+aluminium+tubes+subjectedto+axial+and+oblique+quasistatic+loading

INTRODUCTION
Lightweight materials such as aluminium alloys have become increasingly attractive in the automotive industry. The reason for this is twofold. First, the weight saving using lightweight materials can be considerable compared to conventional steel structures. This will reduce the fuel consumption of the vehicle, resulting in an environmental benefit. Secondly, some aluminium alloys are good energy absorbers during structural impact. Therefore, aluminium alloys are today frequently found in bumper beams and crash boxes to absorb the kinetic energy in accidental car crashes [1] [2]. The increased interest for automotive safety and crashworthiness has resulted in an extensive research into the structural response of thin-walled tubes subjected
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IJCrash 2003 Vol. 8 No. 5 pp. 481–494
© Woodhead Publishing Ltd
0254
T Børvik, O S Hopperstad, A Reyes, M Langseth, G Solomos and T Dyngeland
foams in the explicit finite element code LS-DYNA [24]. The foam model is based on the model proposed by Deshpande and Fleck [25] and adopts, in addition, a statistical distribution of the material parameters to account for heterogeneity of the foam properties (Reyes et al. [26]). Simple failure criteria coupled with element erosion are used to model fracture in the foam when subjected to predominant tensile stresses. The material constants were determined for aluminium foam of different densities, and the foam model was validated against existing and new experimental data for foam specimens and structural components made of foam-filled aluminium extrusions. Finite element simulations by Reyes [2] showed that the model for both empty and foam-filled square extrusions was able to predict the loads with reasonably good accuracy. In this paper, an experimental programme on axial crushing and oblique loading of empty and foam-filled circular aluminium tubes has been completed, and the main results from this investigation are presented. The load angle was varied in the experiments, while the material and geometry of the tubes were held constant. The aluminium foam was of medium density. The response parameters were the peak force, the absorbed energy and the mean crush force, in addition to visual observations of the deformation mode and fracture. Finally, numerical results from LS-DYNA simulations of empty and foamfilled columns are presented, in which the DeshpandeFleck model has been adopted for the aluminium foam.
Empty and foam-filled circular aluminium tubes subjected to axial and oblique quasistatic loading
T Børvika, O S Hopperstada, A Reyesa, M Langsetha, G Solomosb and T Dyngelandb
to various loading conditions [3]-[23]. While most of the earlier research focused on situations involving pure axial crushing or pure bending of empty extrusions, recent studies have indicated that the mean force and energy absorption may increase during quasi-static or dynamic axial crushing by adding aluminium foam in the structural element [1]. However, during a crash event the loading condition is neither pure axial nor pure bending, but rather a combination of the two. Reyes [2] and Reyes et al. [3] have carried out an extensive experimental and numerical study on the structural behaviour of both empty and foamfilled aluminium extrusions subjected to quasi-static oblique loading. It was found that only a small load angle decreased the energy absorption capability considerably. Only square extrusions were investigated by Reyes. The main objective of the present study is to extend this work by investigating the structural response of empty and foamfilled circular tubes subjected to axial and oblique quasistatic loading. Reyes [2] implemented a constitutive model for metallic
a
Structural Impact Laboratory (SIMLab), Dept. of Structural Engineering, NTNU, N-7491 Trondheim, Norway b European Laboratory for Structural Assessment, Institute for the Protection and Security of the Citizen (IPSC), European Commission - Joint Research Centre, I-21020 Ispra, Italy
Abstract: Tests on tubular columns made of the aluminium alloy 6060-T4 under axial and oblique,
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quasi-static loading have been performed. The columns were fixed at one extremity, while a concentrated force was applied at the other through a rigid collar. Empty and foam-filled columns were tested for load angles equal to 0, 5, 15 and 30 degrees with respect to the longitudinal direction of the column. The column’s outer diameter was 80 mm and the thickness was 1.5 mm, while the distance from the point of load application to the fixed support was 245 mm. The aluminium foam density was about 0.3 g/cm3. The response parameters were the peak force, the absorbed energy and the mean crush force, in addition to visual observations of the deformation mode and fracture. Furthermore, LSDYNA simulations of the experiments were performed. The columns were modelled with shell elements, while brick elements were used to model the aluminium foam core. The aluminium alloy was modelled using an isotropic elastoplastic model with isotropic strain hardening. Fracture in the aluminium column was not considered in the simulations. The aluminium foam was modelled using the Deshpande-Fleck model. In selected simulations, fracture was assumed to occur at a critical value of the plastic volumetric strain. The agreement between the experimental and predicted results was in general good.